Not applicable.
Not applicable.
The present invention relates generally to portable computers and particularly to battery operated portable computers. More particularly, the present invention relates to automatically calibrating batteries in portable computers.
Effective battery design has been at the forefront of computer systems development in recent years. Batteries store electric charge, which is gradually released to power the computer circuitry. Laptop computers in particular are designed to operate on battery power, allowing the computer to be used in virtually any location. Because the user is limited to a finite number of hours of computing time before the battery runs out, a longer lasting battery generally provides the user with a more fulfilling and productive experience. The exact amount of operating time that a battery provides depends on a number of factors, including the charge storage capacity of the battery, the operating speed of the computer, and the number of transistors in the computer. Higher operating speeds and more transistors, which generally permit higher performance, generally draw more power. Thus, power requirements continue to increase as computer manufacturers strive to improve performance, increasing the demand for higher battery capacity. Increasing battery storage capacity usually increases the size and weight of the battery, however, and large, heavy batteries are not feasible for laptop computers due to inherent size and weight restrictions.
Manufacturers have employed a variety of techniques to extend battery operating time, including modifications to computer hardware, special power-saving software algorithms, and improvements in battery technology. Many computer components, especially in laptop computers, are designed to shut down after a period of inactivity, even while the rest of the computer continues to operate. The display screen, for example, may darken or turn off if the user fails to type on the keyboard or move the mouse after a predetermined period of time. Similarly, the disk drive may shut off if not accessed for a period of time. Many computer systems are capable of entering a special xe2x80x9csleepxe2x80x9d mode in which virtually the entire computer shuts down, including the central processing unit (CPU), although the memory contents are retained so that the computer can return to normal operation within a few seconds. Older computers relied on instructions stored in the computer hardware known as the Advanced Power Management (APM) to determine when to shut down selected components. Newer computer designs which conform to the Advanced Configuration and Power Interface (ACPI) standard, developed by Intel, Microsoft, and Toshiba, rely on the operating system (e.g., Windows 98) software to turn individual components on and off. Power control, through either hardware or software, extends the battery life by drawing power only as needed.
Recent improvements in battery design have extended battery life, as well. Previously, battery voltage would gradually decrease as the charge drained, eventually dropping below the required operating voltage of the computer. Although some electric charge would remain, these batteries could not regain the required operating voltage without being recharged. Newer by contrast, tend to remain at the required operating voltage until the charge is almost completely gone. When the battery output voltage drops below the desired operating voltage, modem computers typically have about four to eight seconds of operation time left before power completely vanishes, terminating computer operation. Thus, modem batteries last longer by operating more efficiently.
In order to prevent the computer from suddenly shutting down due to a drained battery, possibly resulting in data loss, computer software continuously tracks the battery level and notifies the user of the remaining battery power. Some computers, upon nearing complete discharge, prevent data loss by automatically saving the memory contents to disk and then shutting the computer down. The user then must recharge the battery, insert another computer battery, or plug the computer into a wall socket to resume computing.
Accordingly, it is desirable to know how much battery charge remains. Typically, the amount of remaining charge is determined by continuously measuring battery output current, beginning after the battery is recharged. Because the exact amount of charge after recharging is difficult to measure accurately, the battery monitor assumes that the battery charges to full capacity after each recharge, where the capacity represents the highest theoretical level of charge that the battery can store. The remaining battery level then is determined by subtracting the spent charge from the total battery charge capacity.
Because of the nature of battery chemistry, however, accurately determining the amount of charge stored in the battery after recharging can prove difficult. Many rechargeable batteries exhibit a phenomenon known as the xe2x80x9cmemory effect,xe2x80x9d in which the battery cannot charge to full capacity unless first being completely discharged. If a battery is discharged to 90% of its initial charge level and then recharged, for example, then recharging the battery will not succeed in filling the battery to 100% of its charge capacity. Instead, the battery will stop recharging before reaching full capacity. Repeated charge/discharge cycles enhance the memory effect, causing the battery to reach successively lower levels of charge after each recharge. Whenever the memory effect prevents the battery from charging to capacity, the battery monitor reflects a higher level of charge than the battery actually stores. The memory effect thus can reduce the accuracy of a battery monitor by increasing the difference between the battery capacity and the actual charge level after recharging. Accordingly, the battery monitor may indicate that there is charge remaining when the battery reaches complete discharge. If the computer fails to save the contents of memory before the battery actually discharges, then data loss may occur.
To compensate for the battery monitor inaccuracy, the computer typically saves memory and shuts down when the charge level falls below a predetermined cutoff point. The cutoff point, which typically represents a percentage of the total battery capacity, is set sufficiently high to prevent unexpected loss of power. Though effective in preventing unexpected shut down, this early shut down technique reduces the amount of operating time for the user. In addition, because the battery never reaches complete discharge, the memory effect circumvents accurate measurement of the charge level by preventing the battery from fully recharging again. For this reason, batteries often must be calibrated by completely charging and then discharging the battery. After recharging the battery from a complete discharge, the battery can store the full charge capacity, and battery charge level measurements can be made accurately.
Discharging the battery, however, can be challenging and inconvenient for many users. Discharging the battery typically requires idling the computer for long periods, waiting for the battery to drain. While waiting for the battery to drain, the user may use the computer, although not without risking data loss when battery discharge causes the computer to shut down. In addition, many users experience difficulty when built-in power management features interfere with the discharging procedure. As explained above, for instance, some power management features force the computer to shut down before the battery completely drains, preventing the battery from fully recharging. Other power management features emit warning beeps or other indicators when the battery is nearly drained. Many inexperienced users turn the computer off, believing the beep indicates that the battery has fully drained. Further, some users procrastinate or avoid battery calibration altogether, exacerbating the calibration problem.
For the foregoing reasons, a computer system capable of automatically calibrating the battery, with little or no user intervention, would greatly improve mobile computing. Such an apparatus, if devised, should operate without interfering with the user experience. Despite the apparent advantages that such a system would provide, no device to date provides these features.
Accordingly, the present invention discloses a computer system with a rechargeable battery, the computer system capable of executing battery calibration to improve the accuracy of the battery""s internal charge monitor. The calibration procedure drains the battery until the battery is nearly discharged, or until the battery reaches approximately 0% of charge capacity. The calibration occurs during normal computer operation, permitting a user to operate the computer without risking power failure when the battery discharges. The computer returns to normal operation if either the AC power or the battery is removed. During the calibration procedure, the computer system prevents power management software from forcing shut down before the battery completely drains.
A preferred embodiment of the computer system includes a power supply that supplies direct current (DC) power to the computer from an alternating current (AC) source and a rechargeable battery that supplies DC power to the computer. The battery supplies power directly to a power supply rail in the system, and the power supply delivers power to the system power rail through a switch. If the switch is opened, decoupling the power rail from the power supply, then the computer operates from battery power. The power supply generates an AC detect signal which indicates that the power supply is converting AC to DC, even if the switch is opened, preventing DC current flow from the power supply into the computer. The AC detect signal thus indicates when the power supply is operating and capable of powering the computer. The battery generates a master battery status signal while supplying current to power the computer. If additional batteries are included, then only the battery actively powering the computer asserts the master battery signal. The AC detect signal preferably couples to the master battery signal via a switch. If the switch is closed, then the AC detect signal asserts the master battery signal.
A preferred embodiment includes a power management bus bridge or other logic device that manages power control functions in conjunction with a software-based power control protocol, such as ACPI or APM; a state machine that operates the switch coupling the power supply to the computer; and an input/output controller coupled to the battery and to the power management logic. The state machine receives a calibrate signal from the power management logic. As long as the calibrate signal remains deasserted, the state machine holds the switch coupling the power supply to the system power rail closed, permitting current flow from the power supply to the computer. When the calibrate signal is asserted, the state machine opens the switch coupling the power supply to the computer. Asserting the calibrate signal also opens the switch coupling the AC detect signal to the master battery signal. The input/output controller detects when the master battery signal drops and commands the battery to begin powering the system. In response, the battery asserts the master battery signal and begins providing operating current to the computer.
While feeding on battery power during calibration, the computer may operate normally. Because the AC detect signal is asserted during calibration, power management software does not force the computer to shut down when the battery charge falls below the usual shut down charge threshold. Accordingly, the battery is allowed to discharge nearly completely. If the battery is removed, or if the battery drops the master battery signal, indicating that the battery is nearly drained, then the state machine closes the switch to reconnect the power supply to the computer system, thus providing continuous power to the computer and preventing shut down. The master battery signal serves as a timing signal to the state machine, so that the state machine actuates the switch asynchronously, or immediately in response to the master battery signal. The computer thus begins operating on current from the power supply when the master battery signal drops, without suffering power failure. Because the battery nearly completely discharges, the battery subsequently can be recharged to full capacity, restoring the accuracy of the battery monitor.
The input/output controller also monitors the state of the master battery signal. When the master battery signal drops, the input/output controller generates a system management interrupt to the power management logic. The power management logic releases the calibrate signal in response to the interrupt, recoupling the AC detect signal to the master battery signal. The AC detect signal thus pulls the master battery signal high.
Thus, the present invention comprises a combination of features and advantages that enable it to substantially advance the art by providing a computer system capable of automatically calibrating an internal, rechargeable battery without risking shut down due to power failure, thus permitting normal computer use during calibration, extended operation time, and higher battery monitor accuracy. These and various other characteristics and advantages of the present invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings.